During semiconductor wafer processing, the wafers frequently move through several locations such as: a cassette, a load lock station where the atmosphere around the wafer is purged and the wafer may be etched, a pre-processing station where the wafer may be measured or cleaned, a reactor, and a post-processing station where the wafer is cooled, and the thickness of a deposition layer may be measured. The wafer obviously must be handled in order to move to each location; however, each time the wafer is contacted or jarred, particles may be generated, and the likelihood of backside scratching or contamination by such particles is increased. These wafers can be rendered useless for device fabrication by contamination, abrasion, or damage. Therefore, extreme care is required to support and transport wafers.
U.S. Pat. No. 5,046,909 by Murdoch teaches clipping the wafer onto a retaining ring so that the ring is handled during processing instead of directly handling the wafer. A robotic arm moves the wafer to be engaged with the clips. However, the clips contact both the top and bottom of the wafer, and great precision is required in order to initially engage the wafer with the clips.
U.S. Pat. No. 4,306,731 by Shaw, and U.S. Pat. No. 4,779,877, also by Shaw, teach an apparatus comprising a plate-like support provided with an aperture of a diameter larger than the wafer, and clip means for gripping the edge of the wafer. The leading edge of each clip has an arcuate portion within which the edge of the wafer is retained. However, the Shaw inventions require that the clip must first be spread before receiving the wafer to prevent edgewise abrasion. Thus, these inventions are rather complex because additional parts are needed to actuate the clip, such as a pneumatic cylinder and contact pin.
U.S. Pat. No. 4,473,455 by Dean et al. teaches spring-mounted members disposed around the periphery of an aperture in a wafer-mounting plate. However, once the wafer is retained within the wafer-mounting plate, the wafer cannot be moved with the plate because this invention is only for use of holding the wafer during a processing step.
European Pat. Application (Publication number 0 634 784 A1) by A. Tepman discloses a variable speed wafer exchange robot. However, the design is quite complicated, especially that of the wafer support assembly.
Consequently, a need exists for a simple wafer carrying device which is simple to use, has few parts, transportable through multiple locations, minimizes contact with the wafer, and reduces the potential for particle generation.